This invention relates to a mechanical interlock system used in conjunction with a detachable alternating current (AC) cord which is capable of handling high current needed for electric powered appliances such as drills, saws, irons, hair curling irons, heaters, and the like. The mechanical interlock system prevents arcing between contacts.
Arcing can occur between contacts of a plug and socket of an electric appliance when the plug is removed from the socket while the appliance is turned on. This arcing tends to burn the terminals. In addition, arcing can be a fire hazard.
Several mechanical devices have been developed which attempt to solve the arcing problem. These devices are satisfactory, however, they are complex and uneconomical.
Knickerboker, U.S. Pat. No. 1,727,347, issued Sept. 10, 1929 discloses a plug which incorporates a switch that must be in the "off" position before the plug can be connected to or disconnected from an appliance. A locking pin which is part of the switch and plug combination engages an aperture in the wall of the socket.
Hartwig, U.S. Pat. No. 1,731,417, issued Oct. 15, 1929 discloses a unit in which a flexible arm with a pin for engaging the cord plug is actuated by a switch through a bell crank lever and a pin or rod having a spring.
Wulle, U.S. Pat. No. 1,818,290, issued Aug. 11, 1931 discloses a unit having a rocker latch operating through a linkage to a rotary switch. The connecting rod of the linkage abuts a cam type locking surface such that when the switch is on, the rod is retracted allowing the latch to engage a recess in the plug, preventing removal of the plug.
Parish, U.S. Pat. No. 2,705,266, issued Mar. 29, 1955 discloses a switch and receptacle unit in which a lever on the outside of the switch casing is activated by a linkage system to operate an enclosed switch and, at the same time, cause a locking pin to engage a recess in the plug when it is inserted into the receptacle, preventing removal of the plug while the switch is on. In addition, another lock mechanism prevents rotation of the linkage attached to the switch making it impossible to turn the switch on unless a plug is in the receptacle.
Concannon, U.S. Pat. No. 3,372,367, issued Mar. 5, 1968 discloses a single pin plug device in which rotation of a switch operates a cam shaft causing contacts to connect into the plug. A pin on the contact strip inserts into a receptacle on the plug, locking the plug into the socket.
Knecht, U.S. Pat. No. 4,054,762, issued Oct. 18, 1977 discloses a mechanism which locks a plug into a socket when a switch is on. A rotating sleeve around the socket for a grounding pin of the plug contains an L-shaped slot into which a key lug on the grounding pin will fit when the sleeve is properly aligned. Only when the switch is off will the slot in the sleeve and a corresponding slot in the receptacle allow removal or insertion of the plug into the socket by securing the key lug in the L position of the slot.
None of the references disclose a simple, economically constructed plug and switch mechanism as provided by this invention which prevents arcing wherein a flexible bar with a pin on it is displaced by an on-off switch extension so that when the switch is in the off position, a plug with a recess in it for receiving the pin can be inserted or removed and when the switch is in the on position, the plug cannot be removed or inserted because the pin either holds the plug or blocks it.
It is an object of this invention to provide an economical, structurally simple, connector interlock system which prevents arcing.